1. Field of the Invention
This present invention is directed towards improving a process utilizing a continuous gaseous waste stream (syngas) through a tunnel fermentation system or tunnel bioreactor under anaerobic conditions.
2. Relevant Art
Previous methods and art of waste gas fermentation involved tanks or tower structures containing the fermentation medium such as a Continuously Stirred Reactor (CSTR) and Immobilized Cell Reactor (ICR). Most demonstrated tanks in the art are of the Continuously Stirred Reactor (CSTR) type and keep the incoming syngas in solution longer to prevent large bubble formation because syngas would co-mingle to a larger a larger bubble as it ascended to the surface without agitation. Previous art needed to have the syngas pressurized to 3 atmospheres (42 lbs) for it to be pumped against the force of 20-30 feet of water solution. Once the syngas has surfaced there is no longer any contact with the ethanol producing microbes and the exposed syngas must be separated for its unused components or combusted to make electricity. The present invention allows for the syngas, primarily composed of CO, CO2 and H2, to slowly meander at very low pressures (less than 5 lbs psi) through a tunnel.
Contact with the anaerobic bacterium Clostridium Ijungdahlii or mixture of microbes with the meandering syngas must be accomplished by pumping the microbial aqueous medium and allowing contact above the aqueous medium surface level.
Previous methods in the art of ethanol production from carbon black waste gas have all been in a continuous stirred bioreactor.
Carbon black waste gases are produced as the result of partial oxidation of hydrocarbons with insufficient air to form amorphous carbon, with about 1.2 pounds of carbon monoxide produced per pound of elemental carbon. These waste gases form a serious atmospheric contamination problem but also represent a valuable chemical feedstock resource not presently being recovered.
Previous methods in the art have included carbon black waste gas containing about 14% CO, 17% H2, 4% CO2 and its major component N2 and is agitated by compressed air into a continuous stirred tank reactor and maintained at 37 degrees C., and contains Clostridium Ijungdahlii isolate ER12 ATCC deposit 55380. The gas retention time is maintained at 0.52 min. The aqueous liquid medium containing water, base salts, B-vitamins, a nitrogen source and a sulfide source is fed into the reactor at a liquid dilution rate (defined as the ratio of the liquid flow rate to reactor volume) of 1.05 hr−1. The agitation rate of this reactor is 322 rpm, the temperature is 37 degrees C. and the operating pH is 5.03. Under these conditions, the conversion of CO was 83% and the conversion of H2 was 54%.
Optimal gas retention times in (CSTR) models using agitation were in the range of three minutes and 1000 rpm on the bench scale model. The gas recovery varies with its uptake by the bacteria, which was in turn a function of the cell density. See U.S. Patent Application, J. L. Gaddy, Pub. No. US 2003/0211585 A1, Nov. 13, 2003.
There remains a need in the art of fermentation of industrial gaseous substrates also known as syngas for an improved handling system to allow optimal exposure of syngas for the production of ethanol.